DESCRIPTION

This module is an extremely light-weight, high-performance Moose replacement. It also avoids depending on any XS modules to allow simple deployments. The name Moo is based on the idea that it provides almost -but not quite- two thirds of Moose.

WHY MOO EXISTS

If you want a full object system with a rich Metaprotocol, Moose is already wonderful.

I've tried several times to use Mouse but it's 3x the size of Moo and takes longer to load than most of my Moo based CGI scripts take to run.

If you don't want Moose, you don't want "less metaprotocol" like Mouse, you want "as little as possible" - which means "no metaprotocol", which is what Moo provides.

By Moo 1.0 I intend to have Moo's equivalent of Any::Moose built in - if Moose gets loaded, any Moo class or role will act as a Moose equivalent if treated as such.

Hence - Moo exists as its name - Minimal Object Orientation - with a pledge to make it smooth to upgrade to Moose when you need more than minimal features.

Moo and Moose - NEW, EXPERIMENTAL

If Moo detects Moose being loaded, it will automatically register metaclasses for your Moo and Moo::Role packages, so you should be able to use them in Moose code without it ever realising you aren't using Moose everywhere.

This means that there is no need for anything like Any::Moose for Moo code - Moo and Moose code should simply interoperate without problem. To handle Mouse code, you'll likely need an empty Moo role or class consuming or extending the Mouse stuff since it doesn't register true Moose metaclasses like we do.

However, these features are new as of 0.91.0 (0.091000) so while serviceable, they are absolutely certain to not be 100% yet; please do report bugs.

If you need to disable the metaclass creation, add:

no Moo::sification;

to your code before Moose is loaded, but bear in mind that this switch is currently global and turns the mechanism off entirely, so don't put this in library code, only in a top level script as a temporary measure while you send a bug report.

IMPORTED METHODS

new

BUILDARGS

The default implementation of this method accepts a hash or hash reference of named parameters. If it receives a single argument that isn't a hash reference it throws an error.

You can override this method in your class to handle other types of options passed to the constructor.

This method should always return a hash reference of named options.

BUILD

Define a BUILD method on your class and the constructor will automatically call the BUILD method from parent down to child after the object has been instantiated. Typically this is used for object validation or possibly logging.

DEMOLISH

If you have a DEMOLISH method anywhere in your inheritance hierarchy, a DESTROY method is created on first object construction which will call $instance->DEMOLISH($in_global_destruction) for each DEMOLISH method from child upwards to parents.

Note that the DESTROY method is created on first construction of an object of your class in order to not add overhead to classes without DEMOLISH methods; this may prove slightly surprising if you try and define your own.

IMPORTED SUBROUTINES

extends

Calling extends more than once will REPLACE your superclasses, not add to them like 'use base' would.

with

with 'Some::Role1';

or

with 'Some::Role1', 'Some::Role2';

Composes one or more Moo::Role (or Role::Tiny) roles into the current class. An error will be raised if these roles have conflicting methods.

has

has attr => (
is => 'ro',
);

Declares an attribute for the class.

The options for has are as follows:

is

required, may be ro, lazy, rwp or rw.

ro generates an accessor that dies if you attempt to write to it - i.e. a getter only - by defaulting reader to the name of the attribute.

lazy generates a reader like ro, but also sets lazy to 1 and builder to _build_${attribute_name} to allow on-demand generated attributes. This feature was my attempt to fix my incompetence when originally designing lazy_build, and is also implemented by MooseX::AttributeShortcuts.

rwp generates a reader like ro, but also sets writer to _set_${attribute_name} for attributes that are designed to be written from inside of the class, but read-only from outside. This feature comes from MooseX::AttributeShortcuts.

rw generates a normal getter/setter by defaulting accessor to the name of the attribute.

isa

Takes a coderef which is meant to validate the attribute. Unlike Moose Moo does not include a basic type system, so instead of doing isa => 'Num', one should do

Since Moo does not run the isa check before coerce if a coercion subroutine has been supplied, isa checks are not structural to your code and can, if desired, be omitted on non-debug builds (although if this results in an uncaught bug causing your program to break, the Moo authors guarantee nothing except that you get to keep both halves).

Note that this example is purely illustrative; anything that returns a Moose::Meta::TypeConstraint object or something similar enough to it to make Moose happy is fine.

coerce

Takes a coderef which is meant to coerce the attribute. The basic idea is to do something like the following:

coerce => quote_sub q{
$_[0] + 1 unless $_[0] % 2
},

Note that Moo will always fire your coercion - this is to permit isa entries to be used purely for bug trapping, whereas coercions are always structural to your code. We do, however, apply any supplied isa check after the coercion has run to ensure that it returned a valid value.

Takes a coderef which will get called with $self as its only argument to populate an attribute if no value is supplied to the constructor - or if the attribute is lazy, when the attribute is first retrieved if no value has yet been provided.

Note that if your default is fired during new() there is no guarantee that other attributes have been populated yet so you should not rely on their existence.

Takes a method name which will return true if an attribute has a value.

If you set this to just 1, the predicate is automatically named has_${attr_name} if your attribute's name does not start with an underscore, or <_has_${attr_name_without_the_underscore}> if it does. This feature comes from MooseX::AttributeShortcuts.

builder

Takes a method name which will be called to create the attribute - functions exactly like default except that instead of calling

$default->($self);

Moo will call

$self->$builder;

If you set this to just 1, the predicate is automatically named _build_${attr_name}. This feature comes from MooseX::AttributeShortcuts.

clearer

Takes a method name which will clear the attribute.

If you set this to just 1, the clearer is automatically named clear_${attr_name} if your attribute's name does not start with an underscore, or <_clear_${attr_name_without_the_underscore}> if it does. This feature comes from MooseX::AttributeShortcuts.

lazy

Boolean. Set this if you want values for the attribute to be grabbed lazily. This is usually a good idea if you have a "builder" which requires another attribute to be set.

required

Boolean. Set this if the attribute must be passed on instantiation.

reader

The value of this attribute will be the name of the method to get the value of the attribute. If you like Java style methods, you might set this to get_foo

writer

The value of this attribute will be the name of the method to set the value of the attribute. If you like Java style methods, you might set this to set_foo

weak_ref

Boolean. Set this if you want the reference that the attribute contains to be weakened; use this when circular references are possible, which will cause leaks.

init_arg

Takes the name of the key to look for at instantiation time of the object. A common use of this is to make an underscored attribute have a non-underscored initialization name. undef means that passing the value in on instantiation is ignored.

after

SUB QUOTE AWARE

"quote_sub" in Sub::Quote allows us to create coderefs that are "inlineable," giving us a handy, XS-free speed boost. Any option that is Sub::Quote aware can take advantage of this.

INCOMPATIBILITIES WITH MOOSE

There is no built in type system. isa is verified with a coderef, if you need complex types, just make a library of coderefs, or better yet, functions that return quoted subs. MooX::Types::MooseLike provides a similar API to MooseX::Types::Moose so that you can write

has days_to_live => (is => 'ro', isa => Int);

and have it work with both; it is hoped that providing only subrefs as an API will encourage the use of other type systems as well, since it's probably the weakest part of Moose design-wise.

initializer is not supported in core since the author considers it to be a bad idea but may be supported by an extension in future. Meanwhile trigger or coerce are more likely to be able to fulfill your needs.

There is no meta object. If you need this level of complexity you wanted Moose - Moo succeeds at being small because it explicitly does not provide a metaprotocol. However, if you load Moose, then

documentation will show up in a Moose metaclass created from your class but is otherwise ignored. Then again, Moose ignores it as well, so this is arguably not an incompatibility.

Since coerce does not require isa to be defined but Moose does require it, the metaclass inflation for coerce-alone is a trifle insane and if you attempt to subtype the result will almost certainly break.

Handling of warnings: when you use Moo we enable FATAL warnings. The nearest similar invocation for Moose would be:

use Moose;
use warnings FATAL => "all";

Additionally, Moo supports a set of attribute option shortcuts intended to reduce common boilerplate. The set of shortcuts is the same as in the Moose module MooseX::AttributeShortcuts as of its version 0.009+. So if you: